The invention relates to a scraping device for a rotary tablet press comprising a scraper that is designed to scrape off material for pressing that is located on the top side of a die plate of the rotary tablet press, the die plate rotating relative to the scraper, and comprising a force-generating apparatus that is designed to press the scraper with a predetermined compression against the top side of the die plate. The invention also relates to a rotor for a rotary tablet press, as well as a rotary tablet press.
With rotary tablet presses, it is known to arrange scraping devices downstream from the filling apparatuses in order to scrape off from the die plate excess material for pressing. Known scraping devices have a scraper such as a so-called scraper blade that is pressed onto the top side of the die plate by means of a force-generating apparatus. Excess pressing material located on the die plate rotating under the scraper blade is then scraped off inward or outward by the scraper blade from the top side of the die plate. The material to be pressed can, for example, be a powder or pellets, or the like.
With known scraping devices, the scraper bar can be pressed onto the die plate by means of spring force. For this, the force-generating apparatus has a suitable spring. A disadvantage is that the spring force remains fixed due to the properties of the spring, especially its spring constant and its designed arrangement. It is only possible to adapt the spring force to different operating and/or installation situations with significant design effort. Furthermore, the compression from the use of a spring is not specifically defined when there are changes to the operating situation. For example, the scraper blade wears during operation which changes the compression against the top side of the die plate. The force-generating apparatus then must be manually adjusted. Such a manual adjustment or a change in the installation situation can lead to undefined changes in the compression.
On the basis of the presented prior art, the object of the invention is to provide a scraping device, a rotor and a rotary tablet press of the initially-cited type by means of which a specific scraper device compression exists at all times, wherein it is possible to easily flexibly adapt the scraping device to different operating situations and/or installations.
The invention achieves the object with a scraping device of the initially-cited type in that the force-generating apparatus comprises a fluid pillow filled with a fluid that is in contact with the scraper directly or via at least one transmission element in order to press the scraper by a predetermined compression against the top side of the die plate.
The scraper of the scraping device according to the invention can be a scraper blade. The scraper is arranged stationary in a known manner in the direction of rotation of the die plate behind the filling apparatus, also arranged in a stationary manner, for the rotary tablet press. The filling apparatus can in particular comprise a so-called filling shoe. The die plate with its die holes runs under the filling shoe, wherein the die holes are filled with the material for pressing such as a powder, or pellets, or the like. The scraper scrapes off excess material in a known manner that is on the top side of the die plate in the filling apparatus, at least out of the area of the pitch circle in which the die holes are arranged. At least one scraping edge of the scraper facing the excess material during operation is generally arranged at an angle relative to the radial direction with reference to the die plate. The scraper can completely scrape off the material from the die plate. It is however also possible to scrape off the material into an edge area of the die plate that is inactive during subsequent pressing. The excess material can be scraped off inward or outward in a known manner.
For scraping, the scraper is pressed by a force-generating apparatus onto the top side of the rotating die plate. According to the invention, the force-generating apparatus has a liquid pillow in which a fluid is under pressure. The fluid pillow presses the scraper directly or via at least one transmission element and thereby presses it against the top side of the die plate. The compression is generated by the fluid pressure predominating in the fluid pillow. In particular, the fluid pillow has an elastic case and expands according to the pressure predominating in the fluid pillow. This in turn leads to pressure being exerted on the scraper, or compression being exerted on the scraper. The scraper is in turn thereby pressed against the die plate. A constant compression is hence generated against the die plate independent of a level of wear of the scraper. In addition, by appropriately adjusting the fluid pressure predominating in the fluid pillow, a specific compression is generated in a particularly easy manner that can be flexibly adapted to different operating situations and/or installation situations.
It is possible in principle for the fluid pillow to be a liquid pillow filled with a liquid. According to one particularly practical embodiment, the fluid pillow can, however, be a gas pillow filled with a gas. In another particularly practical manner, the gas pillow can be an air pillow in which air is under pressure. The scraper is hence pressed pneumatically against the top side of the die plate.
According to one embodiment, the fluid pillow can be arranged in a housing, wherein the housing possesses at least one opening through which the fluid pillow is in contact with the scraper directly or by means of the at least one transmission element. The housing can, for example, consist of a metal material or plastic. Through the opening, there is a direct contact, or indirect contact via one or several transmission elements, between the fluid pillow and the scraper, whereby the scraper is pressed against the die plate. In particular, a side of the housing opposite at least one opening is closed. The corresponding housing wall that is substantially inflexible forms a counter-bearing against which the fluid pillow braces to exert the compression on the scraper. Almost any form is conceivable for the housing. The housing can for example be designed in the shape of a pot. It can for example possess the shape of a hollow cuboid closed on one side.
According to another embodiment, the force-generating apparatus can also comprise a fluid filling apparatus for filling the fluid pillow with a fluid such as gas. The fluid filling apparatus possesses in particular a control apparatus by means of which the level at which the fluid pillow filled with fluid can be controlled. As mentioned, the fluid pillow can be a gas or air pillow. The fluid pillow is then correspondingly filled with a gas or air by means of the fluid filling apparatus.
According to another embodiment, the force-generating apparatus can also comprise a pressure measuring apparatus that directly or indirectly measures the fluid pressure, such as the gas pressure, predominating in the fluid pillow. The fluid pressure predominating in the fluid pillow permits a direct inference of the pressure exerted by the fluid pillow on the scraper, and hence the compression with which the scraper is pressed against the top side of the die plate. It is therefore particularly easy to monitor the proper compression.
According to another embodiment, the force-generating apparatus can also comprise a fluid regulating apparatus that regulates the fluid filling apparatus to fill the fluid pillow with fluid such as gas depending on the measurements from the pressure measuring apparatus so that a specific fluid pressure predominates in the fluid pillow. By means of the fluid regulating apparatus, the fluid pressure in the fluid pillow, and hence the compression with which the scraper is pressed against the top side of the die plate, can be set to a constant value and maintained at this constant value. It is hence ensured that the scraper always presses against the top side of the die plate with a constant compression or constant pressure. The compression of the scraper is clearly specified at all times.
At the same time, it is possible in a particularly advantageous manner to regulate the fluid pressure in the fluid pillow to different values by means of the fluid control apparatus, i.e., for example to vary the fluid pressure depending on the purpose or place of use. On the one hand, it is therefore possible to adapt the scraping device in a particularly easy manner to different operating situations of the same rotary tablet press. On the other hand, it is possible to easily adapt the scraping device to different installation situations in the same rotary tablet press, or to use in different rotary tablet presses with different installation situations. This can ensure that the scraper always presses against the die plate with the desired compression, e.g. always with the same compression, even in different operating or installation situations, be it in the same or different rotary tablet presses.
As already mentioned, the invention also relates to a rotor for a rotary tablet press comprising a rotatably drivable die plate with a plurality of die holes, as well as an upper punch seat and a lower punch seat for the upper punch and lower punch of the rotary tablet press rotating with the die plate, and comprising at least one scraping device according to the invention.
As also already mentioned, the invention also relates to a rotary tablet press comprising a rotatably drivable die plate having a plurality of die holes, as well as an upper punch seat and a lower punch seat in which the upper punch and lower punch rotating with the die plate are guided to press material added to the die holes of at least one filling apparatus of the rotary tablet press arranged stationary relative to the die plate, wherein an upper punch and a lower punch are assigned in each case to a die hole, furthermore comprising a rotary drive for rotating the die plate as well as the upper die seat and the lower die seat, and furthermore comprising a scraping device according to the invention.
In a manner known per se, the rotary tablet press according to the invention comprises a pressing station with upper and/or lower compression rollers in which the material is pressed. Furthermore, the rotary tablet press comprises guide apparatuses, so-called guide cams, in a manner known per se for guiding the path of the upper and lower punch. In addition, the rotary tablet press comprises an ejection apparatus in a manner known per se that is also arranged stationary relative to the die plate and in which the pressed products such as tablets are ejected.
The at least one filling apparatus is arranged in a manner known per se in the direction of rotation of the die plate in front of the at least one scraper of the at least one scraping device such that material added to the at least one filling apparatus can be scraped off by the following scraper while the die plate rotates. The at least one pressing station of the rotary tablet press is correspondingly downstream from the scraper in the direction of rotation of the die plate in a manner known per se. If a plurality of filling apparatuses are provided, a plurality of scraping devices can correspondingly also be provided, wherein one scraping device is assigned to each filling apparatus. Correspondingly, a plurality of pressing stations assigned to the filling or scraping devices can also be provided. All of this is known and will therefore not be further explained.